(a) Field of the Invention
The present invention relates to a drive motor, and more particularly, to a rotor fixing unit for a drive motor f a rotor to a shaft.
(b) Description of the Related Art
In general, a hybrid vehicle or an electric vehicle, often referred to as an environmentally-friendly vehicle, is driven typically by an electric motor (hereinafter, referred to as a “drive motor”) that produces torque from electrical energy.
Hybrid vehicles are capable of being driven in an electric vehicle (EV) mode, (that is a pure electric vehicle mode which uses only power from the drive motor to operate the vehicle), or in a hybrid electric vehicle (HEV) mode, (using both torque from an engine and torque from the drive motor as power) in order to reduce the amount of emissions which the vehicle produces and decrease fuel consumption. An 1 electric vehicle, on the other hand, is driven using only torque from the drive motor as power and has no other power source.
For example, the drive motor, which is used as a power source for these environmentally-friendly vehicles, is often a permanent magnet synchronous motor (PMSM). A permanent magnet synchronous motor has a stator, a rotor which is disposed to have a predetermined air gap between the stator and the rotor, and permanent magnets which are installed to the rotor. Depending on a method of installing the permanent magnets to the rotor, there are for the most part two types of permanent magnet synchronous motors, a surface permanent magnet motor (SPMM) in which the permanent magnets are installed on a surface of the rotor and an interior permanent magnet synchronous motor (IPMSM) in which the permanent magnets are embedded in the rotor.
In the permanent magnet synchronous motor, a rotor has a rotor core in which a plurality of sheets of steel plates are stacked, and the rotor core is fixed to and installed on an outer circumferential surface of a shaft.
In order to fix the rotor core in a rotation direction, the rotor core has a key protrusion which is formed to be fitted into a keyway that is formed in the outer circumferential surface of the shaft in an axial direction. Therefore, when the key protrusion is fitted into and coupled to the keyway of the shaft in the axial direction, t the rotor core becomes fixed to the outer circumferential surface of the shaft while supporting force in the rotation direction.
In addition, in the related art, in order to fix the rotor core in the axial direction, a retainer is often installed at an end plate side of the rotor core in a press-fit manner. Here, the end plate is made of a material having high magnetic resistance, is interposed between the retainer and the rotor core, and serves to minimize a leakage of magnetic flux. Therefore, when the retainer is installed at the end plate side of the rotor core, the rotor core may be fixed to the outer circumferential surface of the shaft while supporting force in the axial direction without having to worry about the key protrusion coming out of the keyway.
Here, in the aforementioned structure for fixing the rotor core in the axial direction, since materials of the end plate and the shaft are different from each other, the end plate and the shaft are not fixed to each other. As such, when a temperature is varied, the retainer, which is made of the same steel material as the rotor core, is press-fitted between the end plate and the shaft.
However, since this retainer is made of steel that has low magnetic resistance and thus the magnetic flux that is allowed to flow well, the magnetic flux may be leaked from the rotor core to the retainer. This affects the overall performance of the motor.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.